The present invention relates to a method for the crystallization of n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate, to a method for the production of pourable or flowable particles of crystalline n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate and to specific pourable or flowable particles of crystalline n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate.
The effects of sunlight, in particular of UV-B and of UV-A radiation, on the human skin and the skin reactions resulting therefrom, and the options for protecting the skin are for the most part already known and are further investigated in detail (Chemie in unserer Zeit, 2004, 38, 98-112).
Whereas UV-B radiation (290-320 nm) in particular is responsible for the formation of sunburn, UV-A radiation leads to so-called premature skin aging as a result of damage to the collagen and elastin fibers. Furthermore, UV-A radiation is able to damage DNA, which in the worst case scenario can lead to skin cancer.
The industry therefore supplies both so-called UV-B filters and UV-A filters in order to reduce the harmful effects of solar radiation on the human skin.
EP-A-1 046 391 describes the use of amino-substituted hydroxybenzophenones as photostable UV-A filters in cosmetic preparations.
WO 03/097578 describes a method for the production of n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate of the formula I
where the pink-colored crude product produced in the synthesis in crystalline form from solution is firstly purified by chromatography and then freed from the solvents present by distillation. Finally, the clean end product is bottled as melt.
n-Hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate is marketed commercially by BASF Aktiengesellschaft under the trade name Uvinul® A Plus as UV-A filter. Since the product is bottled as melt and first crystal growth occurs after storage for about six weeks at room temperature, the user has to heat the entire pack to a temperature above the melting point of n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate in order then to be able to remove liquid product from the pack.
WO 2005/025529 describes a pulverulent preparation of n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate (Uvinul® A Plus), where the UV-A filter is embedded in modified starch as protective colloid. The dry powder can be redispersed again in water, in which case the UV-A filter is present in colloidally disperse form. The protective colloid has to be tolerated in subsequent applications.